This invention relates to fiber optic (optoelectronic) communications, and more particularly to pluggable fiber optic transceivers utilized in fiber optic systems.
Fiber optic transceivers facilitate bi-directional data transmissions between electronic devices (e.g., computer, input/output system, peripheral device, or switch) and optical data links in fiber optic (optoelectronic) systems. Each transceiver includes a photodetector for converting optically encoded data received from an optical data link to electrically encoded data readable by a host electronic device, and a laser diode for converting electrically encoded data signals from the host electronic device that are converted into optical signals and transmitted to the optical data link. Each transceiver is mounted onto a circuit card assembly of the host electronic device, and is therefore typically packaged such that it occupies as little circuit card surface area as possible.
Small Form-factor Pluggable (SFP) transceivers are one type of transceiver having standardized physical dimensions and performance characteristics that are defined in the xe2x80x9cCooperation Agreement for Small Form-Factor Pluggable Transceiversxe2x80x9d, as executed on Sep. 14, 2000 (herein xe2x80x9cthe Cooperation Agreementxe2x80x9d), which is incorporated herein in its entirety. The Cooperation Agreement is part of an SFP Transceiver multi-source agreement whose purpose is to establish internationally compatible sources of pluggable fiber optic transceivers in support of established standards for fiber optic systems. Specifically, the Cooperation Agreement sets forth transceiver package dimensions, cage and electrical connector specifications, host circuit board layouts, electrical interface specifications, and front panel bezel requirements that are followed by each party.
As set forth in the Cooperation Agreement, the transceiver electronics of each SFP Transceiver are mounted in an elongated transceiver housing that is designed for xe2x80x9cpluggablexe2x80x9d insertion into a cage assembly. The cage assembly is mounted onto a host circuit board over a female electrical connector, and includes a front opening for receiving the transceiver housing. The transceiver housing includes a male connector board located at a back end thereof that is plugged into the female electrical connector when the transceiver housing is inserted into the cage. Located at a front end of the transceiver housing are receptacles for receiving standard optical connectors (e.g., duplex LC, MT-RJ, or SG connectors).
The cage assembly, as described in the Cooperation Agreement, includes a bottom portion that is soldered to a host circuit board, and a top portion that is detachably mounted onto the bottom portion after soldering. Soldering is used to provide electrical connection between the host circuit board and the cage assembly, which serves a ground plane for the SFP transceiver inserted therein. The top and bottom portions are stamped or otherwise cut from thin sheet metal, folded along predetermined fold lines and then coupled to form the lower, side, and upper walls of the cage assembly. The lower wall, which is part of the bottom portion, defines an opening through which the female electrical connector extends when the bottom portion is soldered to the host circuit board. The side walls extend upward from the lower wall, and support the upper and back walls when the top portion is mounted on the bottom portion. The front opening of the cage assembly, through which the SFP transceiver is inserted, is defined by the lower, upper and side walls when the top portion is mounted on the bottom portion.
Recently, several problems with the conventional cage assembly have become apparent to those who install and maintain SPF transceivers.
First, the soldering process needed to connect the bottom portion of the cage assembly to a host circuit board introduces a time consuming processing step that significantly increases production costs. Further, if the bottom portion is damaged after soldering, the entire host board, which often includes several tens of SPF transceivers, must be taken xe2x80x9coff linexe2x80x9d in order to remove the solder connecting the damaged bottom portion to the host circuit board.
A second problem associated with the conventional cage assembly is that mounting the top portion onto the bottom portion requires a time consuming and tedious manual assembly operation that can result in damage to the cage assembly and/or the female electrical connector. Note that the detachable top portion allows access to the female electrical connector for troubleshooting purposes without having to remove the bottom portion, which is soldered to the host circuit board. However, the need to remove cage assembly top portions for troubleshooting female electrical connectors occurs infrequently, but the manual assembly operation must be performed each time a cage assembly is initially installed on a host circuit board.
What is needed is a mechanism for connecting a pluggable fiber optic transceiver cage to a host circuit board that both avoids the soldering step and provides the necessary electrical (ground) connection between the cage and the host circuit board. What is also needed is a cage that avoids the manual assembly operation while facilitating convenient access to the female electrical connector after installation.
The present invention is directed to a single-piece (integral) cage for pluggable fiber optic transceivers that is easy to install on and remove from a host circuit board. The cage includes side walls that are integrally connected along upper fold lines to a top wall, and one side wall is integrally connected along another fold line to a bottom wall. A back wall is integrally connected to the top wall by yet another fold line. An opening is provided in the bottom wall such that the cage can be mounted as a single unit over a female connector, which becomes enclosed by the top, side and back walls. The side, top, and bottom walls are arranged to form a front opening through which a pluggable fiber optic transceiver can be inserted to connect with the female connector.
In accordance with an aspect of the present invention, the single-piece cage is formed from a single blank that is stamped from sheet metal and folded along predetermined fold lines and secured by a latching mechanism. A first portion of the latch mechanism (e.g., a tab having a central opening) extends from a first edge of the blank, which in one embodiment is located on a bottom wall of the cage. A second portion of the latching mechanism is formed by bending a tab that is located adjacent to a second edge of the blank, which in one embodiment corresponds to a side wall of the cage. The second portion has a fixed end integrally connected to the side wall, and a free end that extends at a predefined angle relative to the side wall. The first latch portion is bent perpendicular to the bottom wall during the blank folding process, and slides along the free end of the second portion during assembly. When the cage is closed such that the side wall contacts the bottom wall, and the first portion resiliently snaps over the free end of the second portion, which presses against an inner edge of the central opening to lock the cage into the closed position. By forming the entire cage from a single blank that includes the latch structure, the cage is significantly less difficult to install on a host circuit board than conventional two-part cage assemblies that require a tedious manual assembly operation.
In accordance with another aspect of the present invention, a series of feet extend downward from the cage and are pressed into corresponding plated holes provided in the host circuit board, thereby securing the cage to the circuit board without soldering. The feet are integrally formed on the blank during the blank stamping process such that they extend perpendicular to the bottom wall after the folding process. Each foot is has an elongated oval outer edge with a narrow fixed end, a relatively wide central portion, and a narrow free end. Each foot defines an eye-shaped opening that facilitates resilient deformation of the foot when the cage is mounted on the host circuit board. Specifically, the free end of the foot is pressed into a corresponding plated hole on the host circuit board until the wide central portion presses against the sides of the opening. When sufficient pressing force is applied, the eye-shaped opening facilitates a slight resilient deformation of the wide central portion that, when fully inserted into the plated hole, generates sufficient pressing force to secure the cage to the host circuit board. In addition, the pressing force exerted by each foot against the corresponding plated holes produces the necessary electrical (i.e., ground) connection between the cage and the host circuit board. When a particular female electrical connector must be accessed after the cage is mounted on a host circuit board, the cage is conveniently removed by applying sufficient tensile force to pull the feet from their respective plated holes. Accordingly, the feet secure the cage to the host circuit board without requiring solder or other permanent fasteners, thereby facilitating easy and convenient mounting and removal for servicing of the female connector.